Apparatus and method for computing location of a moving beacon using received signal strength and multi-frequencies

ABSTRACT

Provided is an apparatus and method for computing the location of a radio beacon by using received signal strength (RSS) and multiple frequencies. The apparatus and method of the present invention computes the location of a radio beacon without limitation in distance by using multiple frequencies and received signal strength to resolve the problem of phase ambiguity. A radio beacon location computing system includes a plurality of base stations configured to receive signals of multiple frequencies transmitted from the radio beacon, and detect and output phase differences and received signal strength; and a location computing server configured to receive the phase differences and the received signal strength outputted from the respective base stations, acquire calculation distances based on the phase differences, remove phase ambiguity from the calculation distances based on the received signal strength, and compute the location of the radio beacon.

TECHNICAL FIELD

The present invention relates to a radio beacon location computingapparatus and method for determining the location of a radio beacon;and, more particularly, to a radio beacon location computing apparatusthat can determine the location of a radio beacon by receiving signalstransmitted from the radio beacon at a plurality of base stations andusing received signal strength (RSS) and phase difference information ofthe received signals, and a method thereof.

BACKGROUND ART

A general method of tracing the location of a radio beacon will bedescribed hereinafter with reference to the accompanying drawings.

FIG. 1 is an exemplary view showing a typical radio beacon locationcomputing system.

Referring to FIG. 1, a radio beacon 100 transmits signals in two or morefrequencies f1 and f2, which are independent from each other. Then, atleast three base stations 111, 112 and 113 receive the signals in thetwo frequencies, extract phase differences ΔΦ1, ΔΦ2 and ΔΦ3 based on atransmission distance in phase difference calculator 141, 142 and 143,and computes the location of the radio beacon 100 in the locationcomputing server 120 based on the extracted phase differences to therebycompute and determine the location of the radio beacon 100.

Generally, the method that a radio beacon transmits signals in two ormore frequencies and base stations receive the radio signals and computea distance by calculating a phase difference based on a frequencyinterference phenomenon has a problem that the calculation for acquiringa distance between a base station and a radio beacon produces aplurality of solutions where the phase differences between the twofrequencies are ΔΦ, 2π+ΔΦ, 4π+ΔΦ, . . . due to ambiguity of a phaserepeating at a period of 2π.

Accordingly, the conventional radio beacon location tracing method usingmore than two different frequencies and a phase difference thereof has alimited coverage, which is an area where the phase difference betweenthe two frequencies is smaller than 2π. Thus, the conventional methodcannot be applied to an environment where the coverage is larger thanthe phase difference of the two frequencies, i.e., 2π.

Hereinafter, the conventional radio beacon location computing methodusing two frequencies will be described with reference to FIG. 2.

FIG. 2 is a diagram illustrating ambiguity in location computation(positioning ambiguity) caused by phase ambiguity.

One radio beacon (TS) 100 transmits radio signals by using twofrequencies, and base stations RS1, RS2 and RS3 111, 112 and 113covering the area where the radio beacon 100 is disposed measure thephase difference between the two frequencies and computes the distanceto the radio beacon 100. The measured phase differences ΔΦ1, ΔΦ2 and ΔΦ3correspond to distances R1, R2 and R3 210, 220 and 230, respectively.When circles are drawn by taking the distances as radiuses, anintersection 240 where the three circles meet is determined as thelocation of the radio beacon 100.

However, when it is assumed that only the base station RS1 111 has phaseambiguity, it is possible to predict that the radio beacon 100 exists ata location where the phase difference of the two frequencies is 2π+ΔΦ1.Thus, a circle having a distance R1 211 corresponding to 2π+ΔΦ1 as itsradius can be drawn. This method yields a solution of another location250 where circles having the distances R2 and R3 220 and 230 from thebase station RS2 112 and the base station RS3 113 meet.

Therefore, there is a problem that the accurate location of the radiobeacon 100 cannot be detected in an area where the phase differencebetween the two frequencies is larger than 2π.

To sum up, since the conventional location computing method using morethan two frequencies and phase difference at a location where thefrequencies arrive may produce a plurality of solutions due to the phaseambiguity, it should be used within an area where the phase differencebetween the two frequencies is less than 2π. The limitation in distancedraws back the location computation of a radio beacon from enlarginginto an area where the phase difference between the two frequencies islarger than 2π.

DISCLOSURE Technical Problem

It is, therefore, an object of the present invention to provide a radiobeacon location computing apparatus that can compute the location of aradio beacon without limitation in distance by using received signalstrength (RSS) to resolve a phase ambiguity problem occurring in alocation computing method using multiple frequencies, and a methodthereof.

Other objects and advantages of the present invention can be understoodby the following description, and become apparent with reference to theembodiments of the present invention. Also, it is obvious to thoseskilled in the art to which the present invention pertains that theobjects and advantages of the present invention can be realized by themeans as claimed and combinations thereof.

Technical Solution

In accordance with one aspect of the present invention, there isprovided a method for computing a location of a radio beacon by usingreceived signal strength (RSS) and multiple frequencies, which includesthe steps of: a) receiving signals of multiple frequencies in aplurality of base stations from the radio beacon and acquiring signalstrength (s1, . . . , sn) of the received signals; b) receiving phasedifferences ΔΦ1, ΔΦ2 and ΔΦ3 of the multi-frequency signals from thebase stations; c) acquiring calculation distances R1, Rn) based on thephase differences; d) removing phase ambiguity from the calculationdistances by using the received signal strength; and e) determining thelocation of the radio beacon based on the calculation distances deprivedof the phase ambiguity.

In accordance with one aspect of the present invention, there isprovided a system for computing a location of a radio beacon by usingreceived signal strength and multiple frequencies, which includes: aplurality of base stations configured to receive signals of multiplefrequencies transmitted from the radio beacon, and detect and outputphase differences and received signal strength; and a location computingserver configured to receive the phase differences and the receivedsignal strength outputted from the respective base stations, acquirecalculation distances based on the phase differences, remove phaseambiguity from the calculation distances based on the received signalstrength, and compute the location of the radio beacon.

Advantageous Effects

The apparatus and method of the present invention can compute thelocation of a radio beacon without limitation in distance by usingReceived Signal Strength (RSS) along with phase difference of multiplefrequency signals to remove phase ambiguity from a distance acquiredfrom calculation based on phase difference.

DESCRIPTION OF DRAWINGS

The above and other objects and features of the present invention willbecome apparent from the following description of the preferredembodiments given in conjunction with the accompanying drawings, inwhich:

FIG. 1 is an exemplary block view illustrating a typical radio beaconlocation computing system;

FIG. 2 is an exemplary diagram illustrating ambiguity in locationcalculation (positioning ambiguity) caused by phase ambiguity;

FIG. 3 is an exemplary block view illustrating a radio beacon locationcomputing system using Received Signal Strength (RSS) and multiplefrequencies in accordance with an embodiment of the present invention;

FIG. 4 is a flowchart describing a radio beacon location computingmethod using received signal strength and multiple frequencies inaccordance with an embodiment of the present invention; and

FIG. 5 is an exemplary diagram illustrating a phase ambiguity removingprocess in accordance with an embodiment of the present invention.

BEST MODE FOR THE INVENTION

Other objects and aspects of the invention will become apparent from thefollowing description of the embodiments with reference to theaccompanying drawings, which is set forth hereinafter. Also, when it isconsidered that detailed description on a related art to which thepresent invention pertains may obscure the points of the presentinvention, the description will not be provided herein. Hereinafter,specific embodiments of the present invention will be described withreference to the accompanying drawings.

FIG. 3 is an exemplary block view illustrating a radio beacon locationcomputing system using Received Signal Strength (RSS) and multiplefrequencies in accordance with an embodiment of the present invention.

Referring to FIG. 3, the radio beacon location computing system usingreceived signal strength and multiple frequencies includes a radiobeacon (TS) 310, a plurality of base stations RS1, RS2 and RS3 320, anda location computing server 330.

The radio beacon 310 transmits signals in two frequencies f1 and f2.

The base stations 320 receive the signals of two frequencies f1 and f2transmitted from the radio beacon 310, and detects and outputs phasedifferences and received signal strength.

The location computing server 330 receives the phase differences ΔΦ1,ΔΦ2 and ΔΦ3 and signal strengths s1, s2 and s3 of the signalstransmitted from the base stations and computes the location of theradio beacon 310.

The base stations 320 include a receiver 321, a phase differencecalculator 322, and a received signal strength detector 323. Thereceiver 321 is configured to receive the signals transmitted from theradio beacon 310 through an antenna, modulate the signals, and outputthe modulated signals. The phase difference calculator 322 calculatesphase differences between the signals of the two frequencies f1 and f2outputted from the receiver 321 based on a frequency interferencephenomenon. The received signal strength detector 323 receives thesignals of the two frequencies f1 and f2 transmitted from the receiver,detects a signal strength of one frequency f1 or f2, and outputs thesignal strength of the detected frequency.

FIG. 4 is a flowchart describing a radio beacon location computingmethod using received signal strength and multiple frequencies inaccordance with an embodiment of the present invention.

At step S400, a plurality of base stations RS1, RS2 and RS3 receiveradio signals of two frequencies f1 and f2 are received from a radiobeacon.

At step S410, the base stations RS1, RS2 and RS3 detect received signalstrength s1, s2 and s3 of a predetermined frequency among the receivedsignals, and output the signal strength s1, s2 and s3 to the locationcomputing server. Along with the signal strength s1, s2 and s3, at stepS430, phase differences ΔΦ1, ΔΦ2 and ΔΦ3 of the two frequency signalsare calculated and outputted to the location computing server.

At step S420, the location computing server calculates and predictsdistances d1, d2 and d3 to the radio beacon based on the inputted signalstrength s1, s2 and s3.

At step S440, the location computing server calculates a propagationdistance based on the inputted phase differences ΔΦ1, ΔΦ2 and ΔΦ3 andacquires calculation distances R1, R2 and R3.

Subsequently, at step S450, the location computing server removes phaseambiguity from the calculation distances R1, R2 and R3 based on thepredicted distances d1, d2 and d3. The process of removing the phaseambiguity from the calculation distances by using the distancespredicted based on the received signal strength will be described indetail with reference to FIG. 5.

At step S460, the location computing server determines the location ofthe radio beacon based on the calculation distances R1, R2 and R3 whichare deprived of the phase ambiguity.

FIG. 5 is an exemplary diagram illustrating a phase ambiguity removingprocess in accordance with an embodiment of the present invention.

Referring to FIG. 5, the calculation distances R1, R2 and R3 510, 520and 530 are acquired from calculation based on the measured phasedifferences ΔΦ1, ΔΦ2 and ΔΦ3. When circles are drawn to have thecalculation distances as radiuses, the intersection point where thecircumferences of the three circles meet is predicted as the location570 of the radio beacon.

However, when it is assumed that a base station RS1 has phase ambiguity,the location of the radio beacon may be predicted to be R1′ 511 wherethe phase difference between the two frequencies is 2π+ΔΦ1.

Therefore, when a circle having a calculation distance R1′ 511corresponding to 2π+ΔΦ1 as a radius is drawn from the base station RS1,a solution is detected at another location 580 where the circles of thecalculation distances R2 520 and R3 530 predicted at the base stationsRS2 and RS3, respectively, meet.

In short, when it is assumed that the base station RS1 has a phaseambiguity, one of the circles of the calculation distances R1 510 andR1′ 511 obtained based on the phase difference ΔΦ1 should be selected.

Herein, in the present invention, one among the redundant solutionsobtained due to the phase ambiguity is selected as a calculationdistance based on the distance obtained based on the received signalstrength.

When it is assumed that the base station RS1 has phase ambiguity, acalculation distance closer to the circle of the distance d1 540acquired based on the received signal strength is selected. In otherwords, the phase ambiguity is removed by determining the calculationdistance R1 510 which is close to the distance d1 540 is determined as acalculation distance in the present embodiment.

Therefore, the calculation distances from the radio beacon to the basestations RS1, RS2 and RS3 are determined to be R1 510, R2 520 and R3530, and the location of the radio beacon is determined based ontriangulation. To sum up, a point where the three circles formed by thecalculation distances R1 510, R2 520 and R3 530 is finally determined asthe location 570 of the radio beacon.

The method of the present invention described above may be realized as aprogram and stored in computer-readable recording media, such as CD-ROM,RAM, ROM, floppy disks, hard disks, magneto-optical disks, and the like.Since the process can be easily implemented by those of ordinary skillin the art to which the present invention pertains, it will not bedescribed in detail herein.

While the present invention has been described with respect to certainpreferred embodiments, it will be apparent to those skilled in the artthat various changes and modifications may be made without departingfrom the scope of the invention as defined in the following claims.

INDUSTRIAL APPLICABILITY

The present invention is applied to a system for detecting the locationof radio beacons.

1. A method for computing a location of a radio beacon by using receivedsignal strength (RSS) and multiple frequencies, comprising the steps of:a) receiving first and second signals respectively having first andsecond frequencies in a plurality of base stations from the radio beaconand acquiring signal strength (s1, . . . , sn) of the received signals;b) receiving, from the plurality of base stations, phase differencesΔΦ1, ΔΦ2 and ΔΦ3 calculated between the first and second signals havingfirst and second frequencies received in the base stations of theplurality of base stations; c) acquiring calculation distances (R1, . .. , Rn) based on the phase differences, wherein each calculationdistance may correspond to a plurality of solution distances; d)calculating distances (d1, . . . , dn) to the radio beacon based on thereceived signal strength; e) removing phase ambiguity from thecalculation distances by determining, for each calculation distance, thesolution distance among the plurality of solution distances which isclosest to a corresponding calculated distance to the radio beacon; andf) determining the location of the radio beacon based on the determinedcalculation distances deprived of the phase ambiguity.
 2. The method asrecited in claim 1, wherein the step e) includes the steps of: e1)calculating distances (d1, . . . , dn) to the radio beacon based on thereceived signal strength; and e2) removing the phase ambiguity from thecalculation distances by using the distances.
 3. The method as recitedin claim 2, wherein a solution close to the distance is selected as acalculation distance among redundant solutions of the calculationdistance produced due to the phase ambiguity in the step e2).
 4. Themethod as recited in claim 1, wherein an intersection point where aplurality of circles each drawn by taking each base station at a centerand taking the calculation distance deprived of the phase ambiguity as aradius meet is determined as the location of the radio beacon in thestep f).
 5. A system for computing a location of a radio beacon by usingreceived signal strength and multiple frequencies, comprising: aplurality of base stations, each base station configured to receivefirst and second signals respectively having first and secondfrequencies transmitted from the radio beacon, detect and output a phasedifference calculated between the first and second signals having firstand second frequencies, and detect and output received signal strength;and a location computing server configured to receive the phasedifferences and the received signal strength outputted from therespective base stations, acquire calculation distances based on thephase differences, wherein each calculation distance may correspond to aplurality of solution distances, calculate distances from the respectivebase stations to the radio beacon based on the received signal strength,remove phase ambiguity from the calculation distances by determining,for each calculation distance, the solution distance among the pluralityof solution distances which is closest to the corresponding calculateddistance, and compute the location of the radio beacon.
 6. The system asrecited in claim 5, wherein the base stations include: a receiverconfigured to receive signals transmitted from the radio beacon andoutput the received signals; a phase difference calculator configured tocalculate and output phase difference of the received signals; and areceived signal strength detector configured to detect and output thesignal strength of the received signals.
 7. The system as recited inclaim 5, wherein the location computing server calculates distance tothe radio beacon based on the received signal strength, and removes thephase ambiguity from the calculation distance by using the distance.